Handbook-Heat & Heat Treating

Fig. 20-5. Rivets or other irregularities are

not obstacles to the flame-priming head,

whose flame ports are protected by wear-

resistant pads.

Stone-Shaping When subjected to the high heat of the flame, some types of rock, especially granite and quartizite, spall readily. The heat causes such rapid expansion of surface crystals that they break away from the rock mass with- out melting. Commercial use of the oxy-acetylene flame in stonework is rare, although sculptors successfully use the flame to supplement their chisels. However, jet-piercing blowpipes, which burn oxygen and kerosene, are used in several quarries for piercing blast holes and for cutting channels through large rock masses. A larger, more elaborate type of jet-piercing blowpipe is used in drilling blast holes in taconite, the torch iron ore found in huge quantities in northern Minnesota.